Electroplating



Patented Apr. 9, 1940 UNITED STATES.

PATENT OFFICE ELECTROPLATING No Drawing. Application May 26, 1937, Serial No. 144,921

'7 Claims.

This invention relates to the electrodeposition of zinc and is particularly directed to processes and plating solutions wherein a bright, mirrorlike zinc deposit is plated from a cyanide-zinc bath which contains an oxyheterocyclic addition agent and, if desired, a metal brightener, the action of the organic addition agent being modified by the inclusion of a protective colloid.

The electrodeposition of zinc, or electrogal- 1o vanizing, has been rather extensively employed because electrodeposited zinc coatings, in addition to their low cost, display many characteristics which cause them to be particularly desirable as protective finishes. Zinc, being higher in the 16 electromotive series, will protect iron or steel against rust even after appreciable areas of the base metal are exposed, whereas the corrosion of iron or steel is accelerated by such metals as copper, nickel, and chromium. Despite their nu- 20 merous advantages over many commonly used coating materials, electrodeposited zinc coatings have not enjoyed the use they deserve because ordinarily they do not possess and do not retain a pleasing appearance, and, consequently, for

many purposes they are not acceptable.

Most of the known methods of electrodepositing zinc-result in dark colored or dull plates and, even when the deposits at first are fairly satisfactory, they may soon become dark and discolored. The poor appearance of most electrodeposited zinc coatings has limited their use to protective applications, and those working in the art have, for the most part, turned to other protective materials when it was desired to produce a finish of pleasing appearance.

The electrodeposition of zinc has ordinarily been accomplished by the use of either-an acidzinc bath or a cyanide-zinc bath. With neither of these baths has it been possible to obtain satisfactorily smooth and bright deposits, but the acid-zinc bath is more commonly used because it leads to a brighter deposit with a better color than does the cyanide-zinc bath.

While, under favorable conditions, the deposits obtained from acid-zinc baths are relatively white, they are still none too satisfactory because of their relatively coarse crystalline structure.

Numerous attempts have been made to improve the character of zinc deposits obtained from acid baths, and many addition agents, such as glycerine, dextrine, gum tragacanth, licorice,

. naphthalene compounds, and aluminum compounds have been used in conjunction therewith.

While the use of addition agents improved the character of the deposits to some extent, the results were still none too satisfactory.

In addition to the fact that acid-zinc baths do not produce satisfactory deposits, there are numerous other disadvantages attendant upon their use. For one thing, acid-zinc baths have very poor throwing power, and it is exceedingly diflicult satisfactorily to plate irregularly shaped objects. Another disadvantage of acid-zinc baths is their low cathode efiioiency. As zinc is above hydrogen in the electromotive force series of metals, it is theoretically impossible to deposit zinc from acid solutions, but, of course, the rather great overvoltage of hydrogen does permit zinc deposition. Concurrently with the deposition of zinc, however, there is a very considerable evolution of hydrogen.

While the deposits obtained from cyanide-zinc baths are poor in appearance, they have a relatively fine crystalline structure. A few addition agents, such as alum, gum arabic, and fluorides, have been tried in cyanide-zinc baths, but the results obtained 'were none too satisfactory. Aside from the poor appearance of deposits obtainable therefrom, cyanide-zinc baths have a number of advantageous characteristics. They have good throwing power, and it is therefore possible to deposit a relatively uniform zinc coating on irregularly shaped and recessed articles. Cyanide-zinc baths, moreover, have a relatively high cathode efiiciency which, of course, is very advantageous because the electric current applied to the bath is expended less upon the evolution of hydrogen, and more upon the deposition of zinc.

Cyanide-zinc baths have recently been improved by the inclusion of an oxyheterocyclic compound as an organic addition agent. When used at high current densities, a brightening metal such as a molybdenum compound is included in the bath. By the use of such modified cyanidezinc plating baths it is possible to obtain deposits of great brilliance and smoothness.

The use of oxyheterocyclic compounds is rather expensive because of the high cost of these materials. The oxyheterocyclic addition agent needs to be added in considerable amount during the operation of a plating bath moreover since the baths seem to become deficient in addition agents rather quickly. The relatively large amount of addition agents thus required makes these baths somewhat expensive to maintain as well as to install.

The plating of zinc by barrel plating processes presents some peculiar problems which are not solved by the use of oxyheterocyclic addition agents. At the relatively low current densities used in barrel plating the baths are operated very near to the potential below which no zinc deposits and an initial deposit of zinc is but slowly applied to iron or steel articles. The agitation of the work as is practiced in barrel plating further raises the current density required to effect zinc deposition and contributes to the difliculty of securing an initial coating of zinc.

After an initial coating is applied to an article being plated the further deposition of zinc proceeds more quickly and easily because the overvoltage of hydrogen on zinc is greater than on iron. Barrel plating processes thus present as a major problem the securing of an initial coating of zinc in a minimum of time.

Cyanide-zinc plating baths employing oxyheterocyclic compounds are not as bright at low current densities as they are at higher current densities. This is a considerable disadvantage when objects are to be plated in a barrel plating process wherein very low current densities are used.

I have found that many of the difliculties experienced when using oxyheterocyclic addition agents in cyanide-zinc plating baths can be obviated by the use of a protective colloid.

The combination of a protective colloid with an oxyheterocyclic addition agent markedly reduces the time required to secure an initial coating of zinc. The employment of a protective colloid in a cyanide-zinc bath containing an oxyheterocyclic addition agent thus profoundly modifies the bath making it less expensive to operate and making it particularly suitablefor use in barrel plating processes.

By using a protective colloid with an oxyheterocyclic addition agent the further advantage is secured that smaller amounts of the addition agent are required. This is particularly surprising when it is considered that the protective colloids usually have little effect when used alone as addition agents, and frequently are deleterious. In addition to decreasing the amount of oxyheterocyclic compound initially required, a protective colloid also decreases the rate at which the addition agent is used up.

When used with oxyheterocyclic addition agents, protective colloids frequently increase the brightness of deposits at very low current densities. This effect is not obtained with all protective colloids as will be noted hereinafter, but the advantages of increased brightness are of minor importance compared with the advantageous modification of bath characteristics permitting quick and easy obtention of an initial covering of zinc.

According to my invention, a protective colloid is used with any oxyheterocyclic addition agent. The oxyheterocyclic addition agent should retain its oxyheterocyclic structure in a cyanide-zinc plating bath and should be at least to some extent soluble in the bath. It is to be noted that an oxyheterocyclic compound not readily soluble may often be more satisfactorily dissolved by adding it in a solvent such as alcohol or acetone.

oxyheterocyclic aldehydes may frequently be added most advantageously in the form of a sodium bisulfite addition compound. Piperonal, for instance, is ordinarily diificultly soluble in a plating bath and in water but piperonal-bisulfite is easily soluble in .water. When piperonal-bisulflte in water solution is added to a bath the piperonal is released from the addition compound in ylxanthene, fluorescein,

very finely divided form and thus readily dissolves.

As examples of oxyheterocyclic compounds, I may mention piperonal, plperonyl alcohol, piperonylic acid, piperine, safrole, piperonal acetophenone, coumarin, furfural, furfuran, pyronine, tetrahydrofurfuryl alcohol, hydrofurfuramide, paraldol, ethyl furoate, methyl furoate, furfuralamine, tetrahydrofurfurylamine, dihydroxymethmorpholine ethanol, phenyl morpholine hydrochloride, butyl morpholine hydrochloride, diphenylene oxide, cyclohexene oxide, glycol formal, coumalic acid, and furfuramide.

While, as indicated, any oxyheterocyclic addition agents may be used, it is preferred to use an oxyheterocyclic compound characterized by the presence of a methylenedioxyphenyl group such as piperonal.

According to my invention, the action of an oxyheterocyclic addition agent is modified by the use in conjunction therewith of a protective colloid such as gelatin, gum arable, gum tragacanth, and agar-agar. While such protective colloids are for the most part without effect when used alone in a plating bath, they profoundly modify the characteristics of oxyheterocyclic addition agents.

If desired, a metal brightener may be used in conjunction with the combination of oxyheterocyclic compound and protective colloid. The use of metal brighteners is most beneficial when it is desired to use the baths for plating at relatively high current densities. When it is desired to use a metal brightener, there may be included in the bath a soluble compound of a metal such as molybdenum, chromium, cobalt, manganese, nickel, iron, titanium, rhenium, aluminum, and tungsten.

In the following examples unless otherwise noted a cyanide-zinc bath of the following composition was used:

Grams per liter Zinc cyanide (Zn(CN)-z) Sodium hydroxide (NaOH) 78 Sodium cyanide (NaCN) 42 At the time the bath was made up, two and fivetenths grams per liter of zinc dust was added together with the bath constituents. The zinc dust effected a removal of deleterious impurities from the bath.

To observe the effect of a bright dip, some of the deposits were subjected to the action of a one-fourth per cent solution of nitric acid for about fifteen seconds. Other acidic oxidizing bright dips could, of course, have been used with Example 1 To a cyanide-zinc plating bath made up as above described, there was added:

Gram per liter Piperonal 1 Gelatin 0.1

Zinc deposits were made from this bath with ex cellent results. and on polished copper sheets the deposits were brilliant and lustrous and reproduced reflected images with mirror-like fidelity. A deposit made at a current density of seven amperes per square foot was considerably brighter than a deposit made under similar conditions but omitting gelatin and using three and one-half grams per liter of piperonal. After bright dipping, the deposits were somewhat improved in both cases, but the deposit using only one gram per liter of piperonal with a little gelatin was superior to that made with'three and one-half grams per litergof piperonal only.

The deposit? made using piperonal and gelatin according to this example were considerably less bright at current densities of twenty-five, forty, and eighty amperes per square foot than at seven amperes per square foot, but when the deposits were bright dipped, they were considerably improved and were only a little less bright than the deposit at seven amperes per square foot. This result is in marked contradistinction to the results obtained using piperonal alone at three and one-half grams per liter concentrations wherein deposits considerably less bright were obtained.

A bath composition the same as-that shown above in this example was made but the piperonal was previously mixed with an equimolecular amount of sodium bisulfite. The bisulfite addition compound was a dry, white powder and this was mixed with dry gelatin so that the combined addition agents could readily be added to the bath in predetermined proportions.

To determine the effect of gelatin alone, a cyanide zinc plating bath made up as above described was used with 0.1 gram per liter of gelatin, but omitting the piperonal. This bath gave deposits which at current densities of seven and twenty-five amperes per square foot were less bright than when no addition agent was used. At current densities of forty and eighty amperes per square foot the presence of gelatin caused the zinc deposits to be somewhat better than those which would be obtained without any addition agent. 01" course, none of the deposits obtained were comparable in brightness with those resulting when piperonal was used either alone or with gelatin.

Example 2 Molybdenum trioxide (M003) 7 5 Piperonal 1. Gelatin 0.

Deposits made using this bath were exceedingly brilliant. Bright dipping the deposits made on polished copper sheets effected a barely discernible change, the change appearing perhaps detrimental on deposits made at very low current densities.

A similar bath omitting gelatin and. using three and one-half grams per liter of piperonal gave about the same results as this bath at a current density of forty amperes per square foot. The bath including gelatin gave deposits at seven and twenty-five amperes per square foot as bright as were obtained at forty amperes per square foot with the bath omitting gelatin, and

were of course considerably brighter than the plates obtainable from the bath omitting gelatin at the lower current densities.

A number of commercial articles were plated using the bath of this example with excellent results. The bath proved remarkably stable and required very little additional piperonal from time to time to keep it operating in the best possible manner.

The bath of this example has given excellent results in commercial practice. A typical seven hundred gallon barrel plating installation handling four tons of rivets, nuts, bolts, and the like per day has been made using a bath according to this example. The plated work is uniform and bright and no bright dip is required.

In this same installation and with a bath of the same composition but omitting gelatin, the plated work is not quite as bright and one pound of piperonal is required per day to maintain the bath. With the bath of this example only onethird pound of piperonal and one-eighth pound of gelatin is required to maintain the installation under the same production and same conditions of use.

While the improved brightness is advantageous, and whLe the saving in the amounts'of piperonal used is advantageous, far more important from a commercial standpoint is the reduction in plating time efiected by the use of gelatin.

Using a bath without gelatin in the commercial process referred to, one hour was required to secure an initial covering of zinc. An additional thirty minutes was then required to make the zinc deposit one and one-half to two tenthousandths of an inch thick.

In the same commercial installation under the same conditions but using gelatin according to this example the total plating time was reduced from an hour and a half to only thirty minutes.

Example 3 As a further example illustrating the use of gelatin as a protective colloid but with a different oxyheterocyclic addition agent, a cyanidezinc plating bath was prepared including:

Grams per liter Coumarin 2. 5 Gelatin 0. 1

Zinc deposits made using the bath of this example were of excellent appearance.

The deposits were compared with deposits made from a similar bath omitting gelatin and using three grams per liter of coumarin, and it was found that the use of gelatin caused the deposits to be slightly less bright. This disadvantage was far more than oifset by the savings in addition agent and by the decrease in time required to efiect initial covering of the base.

Example 4 A cyanide-zinc plating bath was made up similar to that of the preceding example as follows:

Grams per liter Zinc cyanide (Zn(CN)z) 60 Sodium hydroxide (NaOH) Sodium cyanide (NaC'N) 40 Molybdenum trioxide (M003) 8.4 Coumarin 2.5

Gelatin 0.1

At the time of mixing the bath 2.4 grams per liter of zinc dust was used to remove deleterious impurities.

Using this bath to plate polished copper sheets and to plate a number of stamped steel articles, excellent results were obtained. The zinc deposits on the polished copper sheets were brilliant and lustrous, and reproduced reflected images with mirror-like fidelity.

The deposits obtained were comparable with deposits made from a similar bath omitting the gelatin and containing three grams per liter of coumarin.

Example 5 A bath similar to those above was made up but using a different oxyheterocyclic addition agent. This bath in addition to the cyanide-zinc bath constituents above mentioned as standard included:

Grams per liter Furfural 6.0 Gelatin 0.1

Zinc deposits made from this bath shortly after the bath was prepared were brilliant and lustrous. The deposits were comparable with those obtained from a similar bath omitting gelatin, tho they were somewhat brighter at a current density of seven amperes per square foot on an un-bright dipped plate.

As furfural is not stable in this type of bath, the bath deteriorated so that after standing over night the results were no longer entirely satisfactory.

Example 6 A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 7.5

Furfural 6.0

Gelatin 0.1

Zinc deposits made on polished copper plates from the bath of this example were extremely brilliant and lustrous, reflecting images with mirror-like fidelity when observed visually. Bright dipping had no discernible effect on the deposits except when the comparison was made in a way to permit extremely accurate observation, in

which case a barely visible difference could be detected. The deposits were considerably brighter than those obtained from a similar bath omitting gelatin. At a current density of seven amperes per square foot the difference was greatest since the bath of this example gave its brightest deposits at this low current density, and since the bath omitting gelatin gave its poorest deposit at the lower current density.

Commercial articles plated from the bath of this example were smooth and bright, and deeply recessed articles were quite uniform.

This bath, like the one of the preceding example, deteriorates upon standing, and it should preferably be used immediately after it is made up.

Example 7 A cyanide-zinc plating bath was made up employing a still different oxyheterocyclic compound in a bath including the following:

Grams per liter Paralidola 5 Gelatin 0.1

Bright and lustrous zinc deposits were obtained using this bath in plating polished copper sheets and in plating commercial stamped steel articles. Deposits made at various current densities were of about the same brightness, and

deeply recessed articles were very uniform in appearance.

The zinc deposits were comparable with those obtained from a similar bath omitting gelatin except that when gelatin was omitted considerably poorer deposits were obtained at a current density of seven amperes per square foot.

Example 8 A cyanide-zinc plating bath similar to that of the preceding example but including a metal brightener was made up with:

Grams per liter Molybdenum trioxide (M003) 7.5 Paraldol 5 Gelatin 0.1

Zinc deposits obtained using the bath of this example were brilliant and lustrous and refiected images with mirror-like fidelity. These deposits were considerably brighter than those of the preceding example, particularly at higher current densities. The deposits obtained were comparable with those obtained using a similar bath but omitting gelatin, except that when gelatin was omitted the deposits were considerably poorer at low current densities than at higher current densities.

Example 9 A similarcyanide-zinc plating bath was made up with:

- Grams per liter Dioxan 6. Gelatin 0.1

Zinc deposits made using the bath of this example were not as bright as those of the preceding examples. The deposits were considerably improved by bright dipping.

Example 10 A similar cyanide-zinc plating bath was made up including a metal brightener as follows:

Grams per liter Molybdenum trioxide (M003) 7.5 Dioxan 6.0 Gelatin 0.1

Zinc deposits made employing the bath of this example were quite satisfactory. It is to be noted, however, that the use of molybdenum did not have an appreciable eifect upon the appearance of the deposit at the lower current densities.

Example 11 Employing a different protective colloid from the one shown above, a cyanide-zinc plating bath was made up according to my invention includmg:

Grams per liter Piperonal 1. Gum arabic 0.3

found that with gum arabic the deposits at higher current densities, around forty to eighty amperes per square foot, were considerably poorer than if gum arabic had not been used. The bath is none-the-less well suited for use as a barrel plating solution wherein moderately low current densities must necessarily be employed.

By the use of gum arabic the amount of piperonal required for the plating of zinc in a brilliant condition at low current densities is greatly decreased, and the solution produces an initial covering coating of zinc much more readily than when gum arabic is not used.

A bath similar to that of the present example was made up including 0.1 gram per liter of gum arabic but omitting the oxyheterocyclic addition agent. When the deposits made thus using gum arabic were compared with those made from the standard bath without addition agents, it was found that the gum arabic had a markedly deleterious action on the bath, the deposits at higher current densities being much duller than if nothing were added, and even at lower current densities there is a rather great decrease in the brightness of the deposit. It is to be noted that at low current densities gum arabic improves the appearance some even tho the brightness is decreased.

Example 12 A bath similar to the one of the precedingv example was made up but using a metal brightener as follows:

Grams per liter Molybdenum trioxide (M003) 7.5 Piperonal 1. Gum arabic 0.3

Zinc deposits made using this bath were comparable with deposits made from a similar bath using three grams per liter of piperonal and omitting gum arabic except that at current densities around eighty amperes per square foot the deposits using gum arabic were somewhat poorer than those of the bath used for comparison.

Example 13 A cyanide-zinc plating bath similar to that of the preceding example but employing a different oxyheterocycllc compound was made up with:

Grams per liter Coumarin 1.25 Gum arabic 0.25

Example 14 A bath similar to that of the preceding example but including a metal brightener was made up with:

Grams per liter Molybdenum trioxide MoOa) '75 Coumarin 1.25 Gum arabic 0.25

Zinc deposits made employing this bath were quite satisfactory at both high and low current densities, tho better results were obtained with current densities from about twenty-five to forty amperes per square foot than were obtained at a current density of seven amperes per square foot. The bath of the preceding example gave somewhat better deposits at low current densities than the bath of this example, particularly on bright dipped plates.

Example 15 A cyanide-zinc plating bath was made up using still a different oxyheterocyclic addition agent with gum arabic:

\ Grams per liter Furfuryl alcohol 6.0 Gum arabic- 0.25

Zinc deposits made using this bath were considerably brighter than deposits made from a similar bath omitting the gum arabic. At current densities much above twenty-five amperes per square foot neither bath gave very bright deposits, and the bath omitting gum arabic gave poor deposits at a current density of twentyfive amperes per square foot.

Example 16 A similar cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 7.5 Furfuryl alcohol 1.25 Gum arabic- 0.25

Example 17 A cyanide-zinc plating bath was made up with: Grams per liter Cyclohexene oxide 0.25 Gum arabic 0.25

Zinc deposits obtained, using the bath of this example were comparable with the zinc deposits obtained from a similar bath omitting gum arabic and using three grams per liter of cyclohexene oxide. The use of three grams per liter of cyclohexene oxide provided an excess because not all of the addition agent was dissolved.

Example 18 A cyanide-zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (M003) 7.5 Cyclohexene oxide 0.25 Gum arabic 0.25

Zinc deposits obtained using this bath were somewhat better than those obtained from a similar bath omitting gum arabic but using three grams per liter of cyclohexene oxide. The advantage of the bath is found, however, not in the slightly increased brightness but in the fact that the gum arabic promotes stability of the cyclohexene oxide, permits deposits with greater ease at low current densities, and reduces the amount of addition agent which must be added to maintain the bath.

Example 19 A cyanide-zinc plating bath particularly well suited for barrel plating processes was made up employing still another protective colloid with a preferred oxyheterocyclic compound:

Grams per liter Piperonal 1.0 Gum tragacanth 0.5

was made up including 0.5 gram per liter of gum tragacanth but omitting the piperonal. It was found that the gum tragacanth effects a very slight improvement at low current densities but is deleterious at higher current densities when thus used alone.

Example A bath similar to that of the foregoing example was made up with:

Grams per liter Molybdenum trioxide (M003) 7.5 Piperonal 1. Gum tragacanth 0.5

Zinc deposits made using this bath were comparable with deposits made from a similar bath using three grams per liter of piperonal and omitting gum tragacanth, except that at higher current densities the baths of this example were poorer.

, Example 21 A cyanide-zinc plating bath was made up with: Grams per liter Coumarin 1.0 Gum tragacanth 0.5

Zinc deposits made employing the bath of this example were comparable with deposits made A from a similar bath using three grams per liter of coumarin and omitting gum tragacanth at low current densities, but the baths of this example gave poor deposits at current densities of forty amperes per square foot and above. I

Example- 22 A similar cyanide-zinc plating bath was made up with:

, Grams per liter Molybdenum trioxide (M003) 7.5

Coumarin 1.0

Gum tragacanth 0.5

Zinc deposits obtained using this bath were almost as bright as deposits obtainable from a bath containing three grams per liter of coumarin but omitting gum tragacanth. This bath is additionally characterized by the economy of addition agent and the stability which results from the use of a protective colloid.

Example 23 still another oxyheterocyclic addition agent including the following:

Grams per liter Tetrahydrofurfuryl alcohol 1. Gum tragacanth 0.5

I Example 24 A bath was made up with:

Grams per liter Molybdenum trioxide (M003) 7.5 Tetrahydrofurfuryl alcohol 1.0 Gum tragacanth 0.5

Zinc deposits made from this bath were moderately satisfactory over a wide range of current densities, tho un-bright dipped deposits were not very good. The deposits obtained from this bath were considerably more successful than those obtained from a similar bath using eight grams per liter of tetrahydrofurfuryl alcohol but omitting gum tragacanth.

Example 25 A cyanide-zinc plating bath employing the oxyheterocyclic addition agent paraldol was made up with:

a Grams per liter Paraldol 5. Gum tragacanth 0.5

Zinc deposits made from this bath were better at low current densities and much poorer at high current densities than deposits made from a similar bath using five grams per liter of paraldol but omitting gum tragacanth.

Example 26 A cyanidezinc plating bath similaroto that of the preceding example was made up but including a metal brightener. The bath of this example included:

Grams per liter Molybdenum trioxide (M003) 7.5 Paraldol 5. Gum tragacanth 0.5

Zinc deposits made using the bath of this example were comparable with those obtained from a similar bath omitting gum tragacanth except that the bath of this example was superior at a current density of seven amperes per square foot.

Example 2? A cyanide-zinc plating bath employing still a different protective colloid with a. preferred oxyheterocyclic addition agent was made up with:

Grams per liter Piperonal 1. Agar-agar 0.5

Zinc deposits made using the baths of this example were considerably brighter than those obtainable from a similar bath using three and onehalf grams per liter of piperonal but omitting the agar-agar. The deposits obtained from this bath were brilliant and lustrous when deposited on polished copper sheets and reflected images with mirror-like fidelity. The bath of this ex- A cyanide-zinc plating bath was made up with ample was used very successfully in a barrel plating process, an initial covering of zinc being quickly obtained. The protective colloid effectually reduced the amount of piperonal required both in making an initial installation ofthe bath and in maintaining it.

A bath was made up using 0.5 grams per liter of agar-agar as the only addition agent. It was found that the agar-agar was somewhat 'detrimental at low current densities and was slightly beneficial at higher current densities.

Example 28 A cyanide-zinc plating bath similar to that of the preceding example was made up with:

Gramsper liter Molybdenum trioxide (M003) 7.5 Piperonal 1. Agar-agar 0.

Zincdeposits made employing this bath were brighter than those of the preceding example at higher current densities as would be expected from the inclusion of the metal brightener. The deposits obtained using the bath of this example were not quite as bright as deposits obtained from a similar bath using three and one-half grams per liter of piperonal but omitting agar-- agar.

Example 29 A cyanide-zinc plating bath was made up with:

Grams per liter Coumarin 1. Agar-agar 0.

Zinc deposits "obtained using the bath of this example were comparable with deposits obtained from a similar bath using three grams per liter of coumarin but omitting agar-agar. In addition to thus permitting the reduction in the amount of oxyheterocyclic addition agent required, the agar-agar also reduced the quantity of addition agent necessary to maintain the bath and also caused the bath to deposit zinc more uniformly at low current densities.

Example 30 A similar zinc plating bath was made up with:

Grams per liter Molybdenum trioxide (MO3) '7. Coumarin 1. Agar-agar 0.

Zinc deposits obtained using the baths of this example were about as bright as deposits made under similar conditions from a similar'bath using three grams per liter of coumarin and omitting agar-agar. This bath would be more suitable than the bath of the preceding example for still plating processes involving the use of higher current densities.

Example 31 A cyanide-zinc plating bath was made up with still another protective colloid, soluble starch (glycogen). The bath of this example was made up with:

Grams perliter Piperonal 1. Soluble starch 0.5

Zinc deposits made using the bath of this example were about as bright as those obtainable using three and one-half grams per liter of piperonal but omitting the soluble starch. -'I'he bath is, of course, particularly valuable because of the advantages for barrel plating arising by reason of the presence of the protective colloid.

A cyanide-zinc plating bath was made up with 0.5 gram per liter of soluble starch and using no other addition agent. The soluble starch was dipped.

trials.

slightly deleterious at low current densities and slightly beneficial at high current densities.

Ezample 32 A cyanide-zinc plating bath was made up with:

, I Grams per liter Molybdenum trioxide (M003) 7. 5

Piperonal 1. Soluble starch 0.5

Zinc deposits made using the bath of this example were exceptionally bright and mirror-like, particularly after the deposits had been bright Un-bright dipped deposits obtained from this bath were slightly less brilliant than un-bright dipped deposits obtained from a similar bath'using three and one-half grams per liter of piperonal but omitting soluble starch.

v Example'33 A cyanide-zinc plating bath was made up with:

Grams per liter Furfural -i 6. Soluble starch 0.

Zinc deposits made employing the bath of this example were about as bright as deposits made from a similar bath omitting the soluble starch.

Example 34 A similar cyanide-zinc plating bath was made up with: I

Grams per liter Molybdenum trioxide (MoO3) '7. 5 Furfural 6. Soluble starch 0. 5

Zinc deposits obtained employing the bath of this example were considerably brighter at all current densities than were the deposits obtained from a similar bath omitting the soluble starch.

While the use of molybdenum as a metal brightener as shown in the foregoing examples ,is preferred, it will 'be understood that other metal brighteners may be used. I may, for instance, add metal brighteners in :the form of such bath-soluble compounds as manganese .sul-

fate, chromium sulfate, potassium ferrocyanide,

cobalt sulfate, nickel sulfate, and aluminum sulfate.

While the specific amounts of oxyheterocyclic addition agents shown are about optimum under the conditions of the examples, it will be understood that I do not intend to be limited thereto since protective colloidsmay be employed with any operative amount of oxyheterocyclic addition agent according to the teachings of my invention with advantage. The amount of oxyheterocyclicv addition agent to use can in each instance best be determined by a few simple of protective colloids indicated above represent about an optimum for the particular conditions of the examples, widely, varying amounts of colloids may be used without departing from the teachings of my lnvention- In general a substantial amount of protective colloid must be used to obtain a benefit and excessive amounts should be avoided because large amounts of colloid tend to cause foaming and to cause streaked and uneven zinc deposits.

It will be appreciated that an increase in the brightness of zinc deposits is not the principal result to be gained by the use of a protective colloid and that the amount to be used cannot be judged on a basis of brightness alone. protective colloid reduces the time required to effect an initial covering of zinc at low current densities and stabilizes the system including the oxyheterocyclic addition agent. The amount of colloid to use is largely governed by consideration of the bath characteristics.

As a practical matter I have found that it is commercially desirable to use about-one-half as much of a protective colloid as the maximum amount which can be used without deleterious effects resulting from the presence of an excess. In general, from about 0.01 gram per liter to about 1.00 gram per liter of a protective colloid will be found satisfactory, tho the specific amount to be used can best be determined by a few simple trials in each individual case.

While the cyanide-zinc baths shown herein are typical, it will 'be understood that the principles of my invention are applicable to any cyanidezinc plating bath. To obtain the best results it;

is desirable that the cyanide-zinc plating bath be as pure as possible and it is particularly desirable that lead compounds be absent.

It will be understood that the specific examples, and groups of materials shown, are intended to be illustrative of the invention and that one skilled in the art may use equivalent materials inwidely varying proportions according to the teachings of my invention without departing from the spirit thereof.

I claim: Y

1. In a process for the electrodeposition of zinc, the step comprising depositing zinc from a cyamide-zinc bath containing in solution'an oxyheterocyclic compound selected from the group consisting of piperonal, piperonyl alcohol, piperonylic acid, piperine, safrole, piperonal acetophenone, coumarin, furfural, furfuran, pyronine, tetrahydrofurfuryl alcohol, hydrofurfuramide, paraldol, ethyl furoate, methyl furoate, furfuralamine, tetrahydrofurfurylamine, dihydroxymethylxanthene, fluorescein, morpholine ethanol, phenyl morpholine hydrochloride, butyl morpholine hydrochloride, diphenylene oxide, cyclohexene oxide, glycol formal, coumalic acid, and fur- 'furamide, and from about 0.01 gram to about 1.0

The

gram per liter of a protective colloid selected from the group consisting of gelatin, gum arabic, gum tragacanth, agar-agar, and soluble starch.

2. A cyanide-zinc plating composition containing a bath-soluble oxyheterocyclic compound selected from the group consisting of piperonal, piperonyl alcohol, piperonylic acid, piperine, safrole, piperonal acetophenone, coumarin, furfur- -al, furfuran, pyronine, tetrahydrofurfuryl alcohol, hydrofurfuramide, paraldol, ethyl furoate, methyl furoate, furfuralamine, tetrahydrofurfurylamine, dihydroxymethylxanthene, fluorescein, morpholine ethanol, phenyl morpholine hydrochloride, butyl morpholine hydrochloride, diphenylene oxide, cyclohexene oxide, glycol formal, coumalic acid, and furfuramide, and from about 0.01 gram to about 1.0 gram per liter of a protective colloid selected from the group consisting of gelatin, gum arabic, gum tragacanth, agar-agar, and soluble starch. v

3. A cyanide-zinc plating composition containing a bath-soluble oxyheterocyclic compound selected from the group consisting of piperonal, piperonyl alcohol, piperonylic acid, piperine, safrole, piperonal acetophenone, coumarin, furfural, furfuran,'pyronine, tetrahydrofurfuryl alcohol, hydrofurfuramide, paraldol, ethyl furoate, methyl furoate, furfuralamine, tetrahydrofurfurylamine, dihydroxymethylxanthene, fluorescein, morpholine ethanol, phenyl morpholine hydrochloride, butyl morpholine hydrochloride, diphenylene oxide, cyclohexene oxide, glycol formal,

'coumalic acid, and furfuramide, from about 0.01

gram to about 1.0 gram per liter of a protective colloid selected from the group consisting of gelatin, gum arabic, gum tragacanth, agar-agar, and soluble starch, and a bath-soluble molybdenum compound.

4. A cyanide-zinc plating composition containing piperonal and from about 0.01 gram to about 1.0 gram per liter of a protective colloid selected from the group consisting of gelatin, gum arabic, gum tragacanth, agar-agar, and soluble starch.

5. A cyanide-zinc plating composition containing coumarin and from about 0.01 gram to about 1.0 gram per liter of a protective colloid selected from the group consisting of gelatin, gum arabic,

gum tragacanth, agar-agar, and soluble starch.

6. A cyanide-zinc plating composition containing safrole and from about 0.01 gram to about 1.0 gram per liter of a protective colloid selected from the group consisting of gelatin, gum arabic, gum tragacanth, agar-agar, and soluble starch.

7. A cyanide-zinc plating composition containing piperonal and from about 0.01 gram to about 1.0 gram per liter of gelatin.

RICHARD O. HULL. 

